Gel electrophoresis, most notably in polyacrylamide gels, is one of the most common laboratory techniques for analyzing biological samples for their protein contents, including both identification and quantitation. Detections of proteins in gels are achieved in a variety of ways. The most common is the use of stains such as COOMASSIE™ Brilliant Blue (BASF Aktiengesellschaft, Ludwigshafen, Germany), Ponceau S (Sigma-Aldrich, St. Louis, Mo., USA), and SYPRO RUBY™ (Life Technologies). Detection can also be achieved without stains, such as by using a stain-free technique disclosed by Edwards et al. in U.S. Pat. No. 7,569,103 B2 (Aug. 4, 2009) and U.S. Pat. No. 8,007,646 B2 (Aug. 30, 2011). These patents describe the UV light-induced reaction between the indole moiety of tryptophan and any of various halo-substituted organic compounds to produce a fluorescent derivative of the protein that emits light at wavelengths in the near-ultraviolet and visible range. The stain-free technique thus entails contacting the proteins or the gel with the halogen-containing reagent, exposing the gel to UV light once the proteins have been separated in bands within the gel by electrophoresis, and detecting, or forming an image of, the emissions from the proteins.